It is common practice to use a hard disk for storing programs and data in a computer. Such a hard disk is heavy, has a large volume, and consumes a large amount of electricity. On the other hand, if a flash memory is used instead of a hard disk, a cache memory is needed. This cache memory is externally attached to the flash memory.
Accordingly, when a flash memory is used instead of a hard disk, the number of components, the weight, the volume, the cost, and the data transfer time are increased because a cache memory is an externally attached component.